The present invention relates to seismic cables and in particular to marine seismic cables. Some marine seismic cables include buoyancy devices --and arrays of such cables are arranged to be towed in a submerged position in the sea behind a surface vessel.
The present invention relates to seismic cables in general and in particular to seabed laid seismic cables. Such cables are arranged to be installed in arrays to cover a certain area on the sea bed. The seismic cables are designed to detect sound wave signals reflected from subsea oil and gas reservoirs when air guns are detonated in the sea.
The seismic cables include a number of sensor devices which are powered and interrogated from a surface vessel. The array of seabed seismic cables may also include electronic units for signal processing. The cables therefore also include power conductors for the electronic units and for the sensors, as well as signal conductors for interconnections and transmitting processed signals detected by the sensors to the vessel.
There will typically be about four sensor groups per 100 meters along the cable, each group containing some 4 sensors. Each sensor group is some 200 mm long.
A typical length of a seabed laid seismic cable is some 100 meters as compared to towed seismic cables having a typical length of some 300 meters. A typical diameter of a cable is some 50 mm. The density of the seabed laid cable is typically 3kg/l which is three times the typical density of a towed seismic cable.